In this study we want to compare giving a new investigational drug called 1592U89 hemisulphate (1592U89) or abacavir in combination with Zidovudine (ZDV) and Lamivudine (3TC) versus the combination of ZDV and 3TC have been tested in adults and children in other studies and have been found safe to use in most patients. These drugs have at times reduced HIV in the patients' blood and increased the number of white blood cells that help the immune system fight infection. Preliminary results suggest 1592U89 is safe and well tolerated. 1592U89, at all doses studied, when administered as single drug or in combination with ZDV, induces a consistent increase in the immune cells (CD4+ cells) and a consistent decrease of HIV in the patients' blood. The purpose of the study is to see which one of the treatments does the best job of reducing the amount of HIV in the blood of children in the study.